The purpose of the Animal Models Core is to provide chronic animals necessary for the projects and insure consistency in animal models across the various projects in this PPG. This will eliminate the variability of preparations and will release the individual Project Directors from the extremely labor intensive task of creating chronic animals and caring for their immediate post operative recovery. The Core will also provide echocardiographic assessment on animals prior to and during the development of heart failure or sham time controls. The Animal Models Core has worked very effectively over the past 10 years of this PPG. Various animal models will be prepared by or under the supervision of Dr. Kurtis G. Cornish who has had many years of experience in the preparation of chronic animals and is experienced in these specific animal preparations. He will be assisted by three technicians in the preparation and care of animals prior to their use by the PPG investigators. The models prepared by this Core will be (1) the coronary ligation model of heart failure (HF) in the rat, and (2) the pacing model of HF in the rabbit. Assessment of the cardiac status of all animals is obtained echocardiographically. The Core is supported by two echocardiographs. Rabbit imaging is done on an Accuson Sequoia 5120 machine and rodent images are obtained on a Visual Sonics Vevo 770. Ms. Johnnie Hackley is primarily responsible for obtaining the data on the rats and rabbits prior to, during and after the induction of heart failure.